1. Field of the Invention
This invention is related to a process and accompanying catalyst for the preparation of glycol aldehyde, and more particularly is related to the preparation of glycol aldehyde from the reaction of formaldehyde, carbon monoxide and hydrogen in the presence of (1) at least one member of a class of rhodium phosphine-amide catalysts in the presence of a wide variety of organic solvents, or (2) at least one member of a class of rhodium phosphine-amine catalysts, either with or without an excess of a triarylphosphine, and also in the presence of a wide variety of solvents, or (3) a wide variety of mixtures of members of classes (1) and (2). The glycol aldehyde product is later hydrogenated to ethylene glycol.
2. Description of the Prior Art
Glycol aldehyde is a valuable intermediate in many organic reactions, and is particularly useful as an intermediate in the production of ethylene glycol through a catalytic hydrogenation process.
Ethylene glycol is a valuable commercial chemical with a wide variety of uses, e.g., as a coolant and antifreeze, monomer for polyester production, solvent, and an intermediate for production of commercial chemicals.
The reaction of formaldehyde with carbon monoxide and hydrogen in the presence of a variety of catalysts at elevated temperatures and superatmospheric pressures is a well known reaction and yields glycol aldehyde, together with methanol, as well as lesser amounts of polyhydroxy compounds which can be subsequently separated by proper separation procedures. For example, U.S. Pat. No. 2,451,333 describes the reaction of formaldehyde, carbon monoxide and hydrogen over a cobalt catalyst to produce ethylene glycol. U.S. Pat. No. 3,920,753 discloses the production of glycol aldehyde by the reaction of formaldehyde, carbon monoxide and hydrogen in the presence of a cobalt catalyst under controlled reaction conditions; however, the process produces relatively low yields of product. Japanese Pat. No. J57-118,527 describes the production of glycol aldehyde using a ruthenium catalyst system. European Pat. No. 002,908 describes a process for the production of glycol aldehyde from the reaction of formaldehyde, in the presence of a rhodium-triphenyl phosphine ligand catalyst, with carbon monoxide and hydrogen, in a tertiary amide solvent. This reference further suggests that glycol aldehyde is preferably extracted from a water immiscible hydroformylation solvent. However, the proposed method suffers from the drawback of limiting the choice of hydroformylation solvent to the class of water immiscible solvents, whereas the most effective hydroformylation solvents, such as acetonitrile, are very water soluble. Furthermore when extracting glycol aldehyde with an aqueous extractant, even when using a water immiscible solvent, a substantial amount of the expensive rhodium catalyst migrates into the water phase and is lost, thereby decreasing the amount and the resultant activity of the remaining catalyst.
U.S. Pat. No. 4,291,179 describes a similar reaction for the production of acetaldehyde in which trifluoroacetic acid is added to produce glycol aldehyde. U.S. Pat. No. 4,356,332 describes the preparation of ethylene glycol from the reaction of synthesis gas and formaldehyde, using a rhodium or cobalt catalyst in the presence of a substantially inert, oxygenated hydrocarbon solvent. European Patent Application 82/200,272.1 describes a process for the preparation of glycol aldehyde which comprises reacting formaldehyde, hydrogen and carbon monoxide in the presence of either a rhodium or cobalt containing catalyst precursor, together with a strong protonic acid, a tertiary amide solvent and a triaryl phosphine, U.S. Pat. No. 4,200,765 describes a process of preparing glycol aldehyde involving reacting formaldehyde, carbon monoxide, and hydrogen in a tertiary amide solvent in the presence of a catalytic amount of rhodium in complex combination with carbon monoxide, using triphenyl phosphine as the preferred catalyst promoter. U.S. Pat. No. 4,405,814 discloses a related process for the production of glycol aldehyde, such process appearing to be as close to applicant's phosphine-amine system as anything currently known, which incorporates a tertiary organophosphorous or arsenic moiety into the rhodium catalyst complex, together with a basic organo amine having a pKa of at least 1.0. The process is flawed by its conversion of a substantial amount of reactant into unwanted high boiling compounds, as well as the need to operate at relatively high pressures. U.S. Pat. No. 4,405,821 discloses another similar process involving carrying out the reaction in the presence of a glycol aldehyde yield enhancing phosphine-oxide. A severe problem associated with several of the just cited processes is that they involve the addition of a base which catalyzes side reactions of the reactants and forms products through the unwanted mechanism of aldol condensation. For example, condensation products such as glyceraldehyde, 1,3 dihydroxypropanone, erythrose, and 1,3 trihydroxybutanone, as well as C.sub.5 and C.sub.6 byproducts have been detected in selectivities of 30 % and more at high conversions, and have thus rendered any commercial process impractical.
Another serious problem to be overcome is that the particularly preferred rhodium-phosphine-amide catalysts disclosed in parent copending U.S. Application Ser. No. 508,704, as well as the earliest prior art catalytic systems which are active in the formaldehyde hydroformylation to glycol aldehyde, are ineffective in catalyzing the subsequent hydrogenation of glycol aldehyde to ethylene glycol. Furthermore, it has been found that the preferred rhodium-phosphine-amides disclosed in Ser. No. 508,704 also have a tendency to migrate into the glycol aldehyde product phase during extraction, and it is essential, both from the standpoint of saving the expensive metal catalyst and also for prolonging the activity of the catalyst, to prevent this migration from occurring. In copending U.S. patent application Ser. No. 597,003, now U.S. Pat. No. 4,496,781, the disclosure of which is incorporated by reference, an improved process has been developed using the particularly preferred lipophilic phosphine-amide catalysts disclosed in Ser. No. 596,994 to extract the glycol aldehyde into an aqueous phase, from which it can be purified and then hydrogenated to the desired ethylene glycol.
A still additional flaw is the necessity for both the prior art catalytic systems, as well as applicant's phosphine-amide class of catalysts, to operate at extremely high pressures, in order to obtain a desirable reaction rate, e.g., about 3800 psi is typical for a most preferred mode of operation, consequently requiring a substantial investment for suitable apparatus. It would be a significant improvement if a catalytic process could be developed which operates effectively at significantly lower pressures; such a process and the attendant financial savings could make the difference between a major commercial success and a failure.
Accordingly, it is an object of this invention to provide an improved process for the hydroformylation of formaldehyde to glycol aldehyde and its subsequent hydrogenation to ethylene glycol, which has high conversions of formaldehyde and fast rates at relatively low pressures, using a variety of organic solvents, from the reaction of formaldehyde, carbon monoxide and hydrogen feedstocks.
It is another object of this invention to provide a process wherein the glycol aldehyde and the transition metalphosphine-amide and/or phosphine-amine catalysts can be easily separated and extracted or recycled from the reaction product mixture in an effective industrial operation.
It is still another object of this invention to develop a hydroformylation catalyst which can effect formaldehyde hydroformylation with a commercially available formaldehyde feed (i.e., 37% formaldehyde in water or 50% in methanol).
It is still another object of this invention to provide a catalyst for the hydroformylation of formaldehyde which is capable of being recycled a substantial number of times without experiencing a significant loss in catalytic activity.